The present invention relates generally to incinerator systems for the abatement of process emissions containing carbonaceous impurities such as volatile organic combustibles (VOC).
Noxious fumes, waste gases or process emissions, which may be termed "feed gas", "waste gas" or "emissions" generally contain volatile organic combustible (VOC) contaminants (carbonaceous impurities). However, the amount of combustible material contained in such emissions is generally below several thousand ppm and, accordingly, will not ignite or propagate a flame at ambient temperature.
Incinerators increase the temperature of such emissions to a level above the ignition temperature of the combustible contaminants by the use of heat derived from a supplemental energy source thereby to oxidize the emission. Regenerative incinerators recover heat remaining in the cleansed exhaust gas to increase the temperature of emissions entering the incinerator thereby minimizing the amount of fuel used by the supplemental energy source to raise the emission to its ignition temperature.
In a typical single unit shell and tube heat exchanger the impure gases flow upwardly through the interior of a plurality of tubes to a combustion chamber. The plurality of tubes are generally affixed to the incinerator as by welding to a tube sheet proximate the combustion chamber. Fuel is burned in the combustion chamber which typically raises the temperature of the impure gases to about 1400.degree. F. (760.degree. C.) where the VOC's are oxidized to CO.sub.2 and H.sub.2 O. The hot gases are then returned to the heat exchanger by downwardly flowing around the outside of the plurality of tubes. However, impure gas flow into the combustion chamber from the ends of the tubes is generally not controlled so as to create a "mixing" effect within the combustion chamber. Because there is no flow control, the amount of time the impure gas remains in the combustion chamber (i.e. "time at temperature") will vary throughout the abatement cycle. A varying "time at temperature" for the impure gas can create the problem of incomplete oxidation of the VOC's.